Posted by Benjamin Roudenis on February 28, 2010 0 comments
This week Eurocopter unveiled its most recent effort to reduce helicopter noise with the radical-looking Blue Edge rotor blade. The new blade has been tested on one of the company’s EC155 helicopters and was shown to reduce noise 3 to 4 decibels, according to the company.
In addition to the Blue Edge rotor blade, the company also introduced something called Blue Pulse technology. Also designed to reduce helicopter noise, the Blue Pulse system uses three flap modules in the trailing edge of each rotor blade. Piezoelectric motors move actuate the flaps 15 to 40 times per second in reduce the “slap noise” often heard when a helicopter is descending.
Both of these technologies are able to reduce noise by minimizing the blade-vortex interaction of the main rotor on a helicopter. Blade-vortex interaction is the source of the pulsating sound most of us are familiar with when helicopters fly overhead. The noise is created when a rotor blade hits the wake vortex left behind from the blade in front of it.
You can listen to a cockpit recording of Eurocopter’s EC155 with and without the Blue Edge rotor below.
Normally, the entire length of the rotor blade interacts with the vortex of the preceding blade. With the Blue Edge rotors, the double-swept tips of the rotor blade reduce the length of the blade-vortex interaction, and it does it at the tip where the blades are moving the fastest relative to the air. The result is a decrease in the sound produced due of the wake interaction at the tip.
Posted by Benjamin Roudenis on February 11, 2010 0 comments
Google is planning to launch an experiment that we hope will make Internet access better and faster for everyone. We plan to test ultra-high speed broadband networks in one or more trial locations across the country. Our networks will deliver Internet speeds more than 100 times faster than what most Americans have access to today, over 1 gigabit per second, fiber-to-the-home connections. We’ll offer service at a competitive price to at least 50,000 and potentially up to 500,000 people.
Posted by Benjamin Roudenis on February 5, 2010 0 comments
A study in the Feb. 5 Science reports that water can freeze at different temperatures depending on whether the surface it rests on is positively or negatively charged. Under certain conditions, water can even freeze as it heats up.
“We are very, very surprised by this result,” says study coauthor Igor Lubomirsky of the Weizmann Institute of Science in Rehovot, Israel. “It means that by controlling surface charge, either positive or negative, you can either suppress ice formation or enhance ice formation.”
. . . . .
With no charge on the surface, the water froze at -12.5º C, on average. But on the positively charged surface, water froze at a relatively balmy -7º. And on a negatively charged surface, ice formed, on average, at a chilly -18º.
. . . . .
Lubomirsky and colleagues also managed to freeze water by heating it. Water droplets stayed liquid at -11º for up to 10 minutes on a negatively charged surface. But after the negative charge dissipated, heating the room to -8º was enough to induce a positive charge in the pyroelectric crystal and freeze the water.
